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Bleeding Time (BT) and Clotting Time (CT)

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Published in Microbiology
Tuesday, 07 June 2016 20:33
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Bleeding Time Bleeding Time
BLEEDING TIME (BT)

The bleeding time test assesses primary hemostasis (vascular and platelet components) and is dependent on adequate functioning of platelets and blood vessels. In this test, a superficial skin puncture or incision is made and the time required for bleeding to stop is measured. Three methods are commonly used: Duke’s, Ivy’s, and template. Duke’s method, which measures bleeding time following ear lobe puncture, is not advocated since it cannot be standardized and can cause a large local hematoma. In Ivy’s method, 3 punctures are made on the volar surface of the forearm with a lancet (cutting depth 2-2.5 mm) under standardized venous pressure (40 mm Hg). A disadvantage with this method is closure of puncture wound before cessation of bleeding. Template method uses a special surgical blade, which makes a larger cut (5 mm long and 1 mm deep). Although template method is better, it can produce a large scar and even a keloid in predisposed individuals. Ivy’s method is described below.
 
Ivy’s Method
 
Principle
Three standard punctures are made with a lancet on the volar surface of the forearm under standard pressure, and the average time required for bleeding to cease from the puncture sites is measured.
 
Equipment
(1) Sphygmomanometer
(2) Sterile disposable lancets (2-2.5 mm blade with shoulder, which limits the depth of penetration).
(3) Stopwatch
(4) Filter paper
 
Method
(1) A sphygmomanometer cuff is wrapped around the upper arm and inflated to 40 mm of Hg.
(2) The dorsal surface of the forearm is cleansed with 70% ethanol and allowed to dry.
(3) Three punctures are made (about 5 cm apart) in quick succession with a lancet (Superficial veins, and scars or bruises should be avoided).
(4) A stopwatch is started as soon as a puncture is made. One stopwatch is needed for each puncture.
(5) Blood oozing from the puncture wound is gently blotted with a filter paper at 15 seconds intervals. Avoid directly touching the edges of the wound.
(6) The timer is stopped when blood no longer stains the filter paper.
(7) Time required for bleeding to cease from all the three puncture wounds is noted. The average time is reported as the bleeding time.
(8) Sterile adhesive strip is applied over the puncture.
 
Normal Range
2-7 minutes. Majority of individuals have bleeding time less than 4 minutes. It should be reported in minutes or nearest half minute. If bleeding continues beyond 20 minutes, BT should be reported as >20 minutes and the test is discontinued.
 
Causes of prolongation of bleeding time
(1) Thrombocytopenia: If platelet count is less than 1,00,000/ml, bleeding time should not be performed, as it will be prolonged. With a very low platelet count, bleeding may be difficult to control.
(2) Disorders of platelet function
(3) von Willebrand disease
(4) Disorders of blood vessels
 
 
CLOTTING TIME

This is a crude test and is now replaced by activated partial thromboplastin time. Clotting time measures the time required for the blood to clot in a glass test tube kept at 37°C. Prolongation of clotting time only occurs in severe deficiency of a clotting factor and is normal in mild or moderate deficiency.
 
REFERENCES
1. Evatt BL, Gibbs WN, Lewis SM, McArthur JR. Fundamental Diagnostic Hematology: The Bleeding and Clotting Disorders (2nd ed), 1992. US Dept. of health and Human Services, Atlanta, Georgia and World Health Organization, Geneva, Switzerland.
2. Lewis SM, Bain BJ, bates I (Eds). Dacie and Lewis Practical Hematology (9th ed). London: Churchill Livingstone, 2002.
3. Provan D, Krentz A. Oxford Handbook of Clinical and Laboratory Investigations (2002). Oxford university Press. Oxford.
Last modified on Tuesday, 07 June 2016 21:16
Dayyal Dg.

Medical Laboratory Technicain at National Institute of Cardiovascular Diseases, Karachi. | Author/Writer/Blogger

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